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MOTILITY OF DENDRITIC SPINES IN THE DEVELOPING
MOUSE VISUAL CORTEX IN VIVO
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| Dendritic spines are the postsynaptic elements of most excitatory
synapses in the mammalian cortex. Spine morphology allows the restriction
of biochemical environments to single synapses, allowing synapse-specific
regulation. Spine shape, however, is highly dynamic. Morphological changes
in spines are developmentally regulated and sensitive to sensory deprivation.
This suggests that spine motility may be important for synaptic plasticity
and circuit development. We have examined spine motility in vivo in the
visual cortex of transgenic mice expressing GFP. Spines on apical dendrites
of layer 5 neurons were imaged through a craniotomy using a two-photon
microscope in anaesthetized animals. To examine the effect of age and
sensory experience, spine shape was monitored by time lapse imaging for
a period of 2 hours. At the ages we studied (P21-P42), we observed significant
changes in spine shape on a time scale of tens of minutes. At these ages
most of the dendritic protrusions have spine-like morphologies, although
some filopodia are also observed. We did not observe significant changes
in spine number, i.e., the appearance of new spines or the disappearance
of existing spines, during the imaging period. We are also examining the
effects of binocular visual deprivation on spine motility during the critical
period for ocular dominance plasticity in the visual cortex. Our data
to date suggest that spines in visually deprived animals also undergo
substantial motility. Supported by: Whiteman Fellowship (AM) and NIH Grant EY11512. |